An inkjet printing device is a fluid ejection device that provides drop-on-demand ejection of fluid droplets through printhead nozzles so as to print images onto a print medium, such as a sheet of paper. It is sometimes desirable to detect characteristics of ink drops ejected by an inkjet printing device. Characteristics of the ink drops may be used to assess the proper operation of the printing device. For example, detecting that ink drops are absent where they should be present and detecting the number, size, shape and/or color of ink drops may help determine whether nozzles through which ink drops are ejected are partially or fully clogged.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.